The development of modern technology requires creating new materials, in particular composites, that constitute a basis for fabricating optical, electronic, and other elements with desired properties.
Composites or composite materials represent systems composed of two or more different components or in other word phases. One of the components is continuous and is called the matrix or base, while the other components are distributed in the matrix in the form of inclusions, in particular particles, fibers, layers, and are referred to as fillers or dispersed phases. A composite material or a composite is a heterogeneous disperse system, the properties of which are not simple combinations of the properties of components. The properties of a composite material can be controlled by modifying the interaction between the matrix and fillers, by selecting proper fillers, and by varying the ratio of components. An important role in obtaining composite materials with desired properties is played by physicochemical parameters of the filler particles.
A composition for obtaining optically transparent materials was disclosed in U.S. Pat. No. 4,143,017 and comprises copolymers containing unsaturated glycols, water, and an organic fillers imparting improved mechanical properties to the final composite, while retaining high optical properties of the components. The fillers represent polyfunctional monomers containing at least one carboxy group, which serve as cross-linking agents.
Various types of the filler molecules containing polymerizable groups were described in the European Patent EP 0,389,420.
Fillers may represent various combinations of substances, which can be organic and/or inorganic. For example, a liquid-crystalline polymer system and an aqueous polymeric dispersion containing both organic and inorganic fillers, were described in PCT patent publications WO 0040655 and WO 0040629. The inorganic components used were alkaline earth metal salts.
Another example of a polymeric composition used in the liquid crystal display backlight system is disclosed in the European Patent EP 0,847,424 and comprises a polymer film covered with a polymeric binder containing both organic and inorganic fillers. The binder is transparent and retains its optical properties for a long time.
The optical properties of a two-component liquid-crystalline system were studied for anisotropic films based on poly(vinyl alcohol) (PVA) modified with iodine [see Bahadur, B., Liquid Crystals: Applications and Uses, ed., Vol. 1, World Scientific, Singapore, N.Y., July 1990, p. 101].
However many optical materials based on polymers, in particular PVA-based films with dye additives, have relatively low thermal stability which put a limit on their application.
A special class of polymers is represented by supramolecular polymers, see for example Brandveld, L., Supramolecular Polymers, Chem. Rev., 101, 4071-97 (2001). The structural units are linked by noncovalent bonds such as hydrogen bonds, complex bonds, and arene-arene bonds. The monomers represent self-assembly discotic molecules, typically of organic dyes, containing various substituted ionic groups. In aqueous solutions, such discotic molecules exhibit aggregation with the formation of a lyotropic liquid crystal.
The important role of intermolecular links of the hydrogen bond type in the formation of supramolecular polymer compositions was described for example in European Patent EP 1,300,447. Such bonds appear as a result of the interaction between functional groups of adjacent polymer chains.
The U.S. Pat. No. 5,730,900 discloses method of obtaining a film comprising polymer matrix. By the disclosed method an initial solution comprises a discotic substituted polycyclic compound containing polymerizable groups in the substituents, and a liquid-crystalline substance. The substrate is an oriented polymer substrate. After the disclosed treatment and further cooling a film is formed comprising polymer matrix with liquid-crystalline inclusions representing the bound filler. This conversion of a two-component mixture leads to the formation of a matrix-polymer system with protection layers, retaining the liquid-crystalline properties in the final film. However, use of organic solvents, the required individual selection of the solvents for the system components, the required high temperatures and/or UV radiation make the aforementioned polymerization process technologically complicated and not environmentally appropriate.
Another class of compounds for the obtaining of modified optical film materials possessing new properties is offered by modified water-soluble dichroic organic dyes with planar molecular structures. Heterocyclic molecules and molecular aggregates of such compounds are characterized by a strong dichroism in the visible spectral range. The process of manufacturing thin crystal films based on such materials does not have the disadvantages of the technology of the art. The manufacturing process includes the following stages. In the first stage, a water-soluble dye forms a lyotropic liquid crystal phase. This phase comprises columnar aggregates composed of discotic molecules of the dichroic dyes [see for example Yeh, P., et al., Molecular Crystalline Thin Film E-Polarizer, Mol. Mater., 14 (2000)]. These molecules are capable of aggregating even in dilute solutions [see Lydon, J., Chromonics, In: Handbook of Liquid Crystals, 1998, pp. 981-1007]. In the second stage, application of the lyotropic liquid crystal phase (in the form of ink or paste) with shear aligns molecular columns in the direction of shear. High thixotropy of the applied liquid crystal provides high molecular ordering in the shear-induced state and its preservation after termination of the shear action. In the third stage of the process, evaporation of the solvent (water) leads to unidirectional crystallization with the formation of an organic solid crystal film from the pre-oriented liquid crystal phase as generally described in the U.S. Pat. No. 6,563,640. Such Thin Crystal Films (TCFs) are characterized by high optical anisotropy of refraction and absorption indices, exhibit the properties of extraordinary polarizers as described in more details in Bobrov, Yu. A., J. Opt. Tehnol., 66, 547(1999), and are available for commercial application in liquid crystal displays as was generally described in Ignatov, L. et al., Society for Information Display, Int. Symp. Digest of Technical Papers, Long Beach, Calif., May 16-18, Vol. XXXI, 834-838 (2000).
The optical anisotropic film manufactured by this technology is limited in the high-humidity environment. As disclosed in U.S. Pat. No. 6,563,640 the films may be additionally treated with the solution containing ion of bi- or tri-valence metals. As the final product of this treatment the non-soluble film is formed. However, the water content can fluctuate with the elevated temperature and high humidity which results in decrease of stability of the optical characteristics.